An electric power system generally comprises the stages of power generation, transmission, distribution and use. Amongst these stages, an electric power network which receives electrical energy from a power transmission grid (or from a local power station), and supplies and distributes electrical energy to users of various types either locally or step by step, is called a power distribution network. A power distribution network generally consists of many types of power distribution equipment and power distribution facilities, and is used for transforming voltages and distributing electrical energy directly to users. Thus, a power distribution network is characterized by a large number of nodes, broad coverage and a complex topological structure.
FIG. 1 shows by way of demonstration a simple example of a power distribution network. As FIG. 1 shows, a power distribution network comprises for example a substation 110 and a power distribution apparatus 120. The substation 110 converts high voltages on a power transmission line to voltages suitable for distribution by the power distribution network (e.g. 35 KV, KV or 220 V). The electrical energy output by the substation 110 is delivered to a power distribution apparatus 120 via a power distribution line. The power distribution apparatus 120 may for example be a distribution station or a distribution switching station, and may also be a pole-mounted switch or switchgear, or another power distribution apparatus or power distribution facility. As FIG. 1 shows, the power distribution apparatus 120 has at least one incoming line L1, and one or more outgoing line (or feeder) L2-L4 (only 3 outgoing lines are shown in the figure by way of demonstration). The incoming line L1 is connected to, for example, an output of the substation 110. The outgoing lines L2-L4 may for example be connected to user terminals of various types, to distribution electrical power to users. A switch 121 in the power distribution apparatus 120 is for example used for switching the connection relationship between the incoming line and the outgoing lines.
In FIG. 1, the substation 110 and power distribution apparatus 120 are also equipped with equipment for achieving automation of power distribution or automatic protection, for example a substation protection (SP) apparatus 112 located at the substation 110 and an automation terminal (AU: terminal unit for automation) 122 located at the power distribution apparatus 120. As FIG. 1 shows, a circuit breaker CB1 for example is also disposed at an outlet of the substation 110, and may be called a substation outlet circuit breaker. The SP 112 monitors the operating situation of a transformer 111 in the substation 110, and the line situation.
In the event of a fault, the SP 112 causes the circuit breaker CB1 to open, or causes the circuit breaker CB1 to realize automated reclosing (AR) as required. Here, the transformer 111 for example converts a high-voltage power transmission voltage, or electrical energy generated by a local power station, to a power distribution voltage, and can be regarded as a source end for electrical energy with respect to a user end.
Similarly, on the side of the power distribution apparatus 120, the switch 121 is connected to the incoming line and outgoing lines, to establish or break the electrical connection between the incoming line and one or more outgoing lines. The switch 121 is for example a pole-mounted switch. Circuit breakers CB2-1-CB2-4 are disposed on the incoming line and outgoing lines L1-L4 respectively.
The AU 122 monitors the state of the incoming line and outgoing lines L1-L4, and in the event of a fault, opens the circuit breaker on the corresponding line. In actual applications, the AU may for example be a power distribution terminal (DTU: distribution terminal unit) mounted on a distribution switching station, and may also be a feeder terminal (FTU: feeder terminal unit) for a pole-mounted switch. The SP 112 and AU 122 in FIG. 1 may also be connected to a power distribution sub-station, or a power distribution main station, via a communication network, to report the operating state of the substation and the power distribution apparatus.
In the network shown in FIG. 1, if a fault occurs on any one of the incoming line or outgoing lines of the power distribution apparatus, the SP 112 will detect the fault on the load line thereof, and thereby cause CB1 to trip. If the substation 110 is provided with an automated reclosing function, the SP 112 can control the CB1 to close automatically after a predetermined waiting time (automated reclosing interval). According to user requirements, the SP 112 can execute automated reclosing multiple times. The maximum number of automated reclosing operations (Nrm: Maximum Number of AR) can be set by a user according to actual requirements, or a system default value may be used.
Due to the provision of automated reclosing, on the power distribution apparatus side it is very difficult to determine quickly and accurately which line has a fault, and whether the fault is a permanent fault which needs to be isolated or a transient fault which can return to normal automatically. This is because the line fault detected on the power distribution apparatus side might for example be an actual outgoing line fault, or a false fault caused by compound fluctuation or interference, or a transient fault existing only for a short time. For this reason, a method and apparatus capable of automatically determining the fault type on the power distribution apparatus side is still needed in the prior art.